TheSamba.com :: View topic - Crankshaft Crossroads

Wed Mar 12, 2025 9:36 am

Sorry for the long post, just getting everything out there hoping you guys can help me narrow down crankshaft/displacement choices for something I'd like to get started on by the end of this month.

Intention was to build a 1955. Universal case is already line bored 1st over, bearings matched to thrust cut, bored for 90.5, stroke clearanced to at least 82 (machinist tells me it's ready for whatever crank I want to install - I know I'll have to verify clearances as I go, no problem there) and 8mm case savers installed. Also full-flowed. So that's pretty much set in stone.

I really want to stay single carb and have two modified 34 PICT-3s, one newer Empi with venturi bored to 28 and currently on the car, and one Bocar that I've recently run at 27.5 venturi but have since bored out to 28.5. After a little tweaking on the jetting and float levels, they both run smooth as butter. Have an OEM center section not currently in use and a CB center section that I've modified by use of some of Alstrup's comments, currently on the car.

After public forum questioning and discussions, and one PM conversation with one of our respected builders, I've concocted my own recipe for end castings and am willing to experiment in that department. Based on what I've been able to pull together, I believe I can break the 90 HP ceiling that the end castings have if not modified.

That covers desired induction. I do know I can do better with duals, and I have a set of DCNFs with manifolds and linkage if I really have to go that way - I just prefer the Solex style center mount even with its known limitations.

I have a locked out German 009 and a Black Box that I've gotten familiarized with programming. Also have a Streetfire CDI and MSD universal 8mm wires that I've cut to length and put tin seals onto the ends, and an MSD 8207 coil (Blaster SS). That covers ignition.

I'm at a moment where I need to strike while the iron is hot, so to speak. CB is out of stock on 76mm 4140 cranks at the moment. Nice price on them, but not currently available and not sure what shipping will be but probably pretty substantial, especially with a matching flywheel. While considerably more expensive, Scat has their 78.8mm 4340 cranks in stock, within easy driving distance (I've picked up many parts at their lobby in the past), and by all accounts on this site, a damn nice crank, maybe the best we have available to us even if overkill for what I want to do. Really nice rods (also in stock) too so might be worth picking it all up from one source.

Using one of modok's posts as a guide, I see why the Scat crank is 78.8 - with stock length rods it should fall to a damn near perfect deck height on an uncut, standard-deck case and B pistons. My case is cut about .6mm at the spigots so I'd need .020 shims to get right at .041 deck if all else works out as it should (I know to actually measure as I go, just looking to plan it out for the least additional machine work as possible - it adds up quick!!)

Now why the question - With the single carb, probable use of heater boxes and 35.5x32 heads that I will have someone qualified build out for me, modified end castings, and a cam maxing out somewhere around 239 duration at .050" (CB 2239 is close, and the JPM that Tabari has listed looks really nice), is the 78.8 crank/2020cc going too far, or is the difference between 1955 and 2020 just purely academic?

And am I close on the cam? I'd like to get all I can in there for as much top end/passing power as reasonably possible while still idling ok on the single carb. A tiny bit of lope is ok. I want it to be as strong as it can be given the constraints above, and in a full-weight Ghia with stock gearing in a late SSC transaxle.

Exhaust I know I will have to pony up for, bit it'll be a while before we get there, so that's ok. The VS SS143 comes highly recommended by many of you for this sort of project, and the CSP Super Comp looks like it might work. Any difficulties with the preheat flow or use of T-stat and flaps with either of them? Any preference between the two? I have a CSP high flow but what I'm building is too much for that muffler. It sure is a nice muffler though, with excellent preheating.

Thanks for any advice you might have!

Wed Mar 12, 2025 10:10 am

2027 cc is a good size. No problems there.
Cam. Do not use a JPM cam in such an engine. JPM makes top of the line race cams, not cams where the engine peaks below 5000. The 2239 would be a good option, or the Nowak 135.
Stock end castings will limit your power to about 90 hp (but I think we covered that already) for a 2 liter the Wensing end castings are too large, so thats it unless you have done your homework on modifying the stock ones.
with stockish end castings the 34 w. 28,5 mm venturi is sufficient. If the end castings can flow some good numbers it is not.
Again, with stockish end castings, detailed stock valved heads are fine. With a better flowing intake a set of "super stock" heads will come in handy. you want more time area at the right side of peak lift.
Both the SS143 and the Supercomp works well in such a combo.
Detailed super stock heads and good end castings and you will soon be in the 100 - 105 hp range, - with a properly shaped 29 mm venturi. A 28,5 will hover juust a hair lower. No issues with the preheat.
Going with a 37 mm and 30 mm venturi (It is thin, I know) along with a properly ported swan neck etc. and you will be between 105 & 110 hp. Still with a stocklike idle.
While it is possible to pull even more power through a 34 mm Solex I typically dont use them on anything larger than 1955 cc because I feel that is where it "tilts" so to speak. A well built 1955 along those lines typically pull 100-105 hp, but the torque suffers a little, no massive numbers, but on the other hand it is long and flat.
I´d say go for the 78,8, and get the right heads and cam. Then you can upgrade carb & induction later, exhaust too. Just don´t choke it with some stupid cheapo muffler.

Wed Mar 12, 2025 10:49 am

Alstrup wrote: 2027 cc is a good size. No problems there.
Cam. Do not use a JPM cam in such an engine. JPM makes top of the line race cams, not cams where the engine peaks below 5000. The 2239 would be a good option, or the Nowak 135.
Stock end castings will limit your power to about 90 hp (but I think we covered that already) for a 2 liter the Wensing end castings are too large, so thats it unless you have done your homework on modifying the stock ones.
with stockish end castings the 34 w. 28,5 mm venturi is sufficient. If the end castings can flow some good numbers it is not.
Again, with stockish end castings, detailed stock valved heads are fine. With a better flowing intake a set of "super stock" heads will come in handy. you want more time area at the right side of peak lift.
Both the SS143 and the Supercomp works well in such a combo.
Detailed super stock heads and good end castings and you will soon be in the 100 - 105 hp range, - with a properly shaped 29 mm venturi. A 28,5 will hover juust a hair lower. No issues with the preheat.
Going with a 37 mm and 30 mm venturi (It is thin, I know) along with a properly ported swan neck etc. and you will be between 105 & 110 hp. Still with a stocklike idle.
While it is possible to pull even more power through a 34 mm Solex I typically dont use them on anything larger than 1955 cc because I feel that is where it "tilts" so to speak. A well built 1955 along those lines typically pull 100-105 hp, but the torque suffers a little, no massive numbers, but on the other hand it is long and flat.
I´d say go for the 78,8, and get the right heads and cam. Then you can upgrade carb & induction later, exhaust too. Just don´t choke it with some stupid cheapo muffler.

This is all TREMENDOUSLY helpful!

Engine size/78.8 crank - will call Scat and see if they actually have it in stock today.
Cam: The Nowak 135 looks like split lift/split duration is that correct? Looks cool but probably a bit harder to get my hands on one of these in the US. Maybe the 2239 will get the nod if it gets me close enough.
End Castings: Yep, we covered that. Thanks for all of the posts in the past that have helped me understand them!
Carb: Great feedback thank you. I'll need to find someone who can take the venturi out to 29 or 30. I maxed out what I can practically do at 28.5 without upping my game on equipment. It's not worth the expense for one or two more venturi cuts.
Center section: You gave me some good advice last time this came up. I saw exactly what you meant and worked the CB center section a bit before I installed it but not to the extent you reccommend for the 37 carb. I think my current engine is too small to tell the difference, but I have not tinkered with ignition timing since the intake install and probably won't for this engine. I can always pick up another center section to play around with: I'm not putting the stock center section back on. Too much trouble with the heat risers routing to where they route...
Heads: Have them worked to match. Hear ya loud and clear on this. I won't be going this one alone.
Torque curve: Long and flat is probably perfect for high gearing. NOT looking to have to build a custom gearbox for any engine I come up with.
Exhaust: Again, hear ya loud and clear!

Thanks very much!!!

Rob

Wed Mar 12, 2025 11:24 am

Talked to CB last night. Cranks are here. They just need to make their way from the dock to Farmersville.

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Wed Mar 12, 2025 11:36 am

Dusty1 wrote: Talked to CB last night. Cranks are here. They just need to make their way from the dock to Farmersville.

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Thanks for the info! This is interesting. Too bad they can't drop one off on their way through - their shipper will probably go within a couple miles of me on the way up.

In all seriousness, I'm probably going to go forward with the Scat, if they return my call sometime within a reasonable time frame and actually have everything in stock as their website says it is. Local pickup makes for a serious value proposition serious shipping cost savings and taking delivery right now before prices have a chance to shift upward is always good.

No problems with the plan thus far means the 78.8mm crank is in play. Thanks again to Torben for clearing that up. I also need to do this once and do it right.

Admittedly, I've at times had a tendency to try to save 48 cants and cost myself 48 dollars. If getting better quality parts, even if overkill for my application, for appx the same money when all costs are considered, I think that might be the way forward.

And overkill is just right!

CB crank/rods/flywheel is the backup plan if Scat doesn't call back or answer the phone when I try to chase them down.

Wed Mar 12, 2025 2:25 pm

Like I said earlier, striking while the iron is hot and the power of now are both powerful forces.

I got through to Scat earlier, and they had a 78.8 forged crank, 12ish lb flywheel, and rod bearings in stock. They didn't have 137mm I Beam rods in stock, but they did have 137mm H Beams.

So I now have in my possession the 78.8 crank, H-beams, and lightened flywheel, ready to go. Time to get started.

Subject Line changed to reflect but not sure if the change is visible.

Wed Mar 12, 2025 2:29 pm

Rob Combs wrote: Subject Line changed to reflect but not sure if the change is visible.
You have t edit your original post, so I did it for you.

Have fun with the build.

Wed Mar 12, 2025 2:30 pm

Thanks Glenn!

Will remember next time.

Sun Mar 16, 2025 9:36 am

Well, I've watched Brian e's TP lifter stock dwindle down to just a few sets, so I got nervous about future stock and went ahead and grabbed a set.

I may have missed something along the way and put the cart in front of the horse - someone please tell me they're compatible with CBs cams. IIRC they're compatible with everything but want to make sure the $$ weren't spent in vain.

We're all in now...

Sun Mar 16, 2025 10:13 am

They are

Sun Mar 16, 2025 10:20 am

Thank you!

Mon Mar 17, 2025 8:31 am

Dusty1 wrote: Talked to CB last night. Cranks are here. They just need to make their way from the dock to Farmersville.

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Just got an email from CB this morning. 76mm cranks are back in stock for those who might be interested. Looks like the price might have gone up by $10. Not too bad...

Mon Mar 17, 2025 9:08 am

Rob Combs wrote: Well, I've watched Brian e's TP lifter stock dwindle down to just a few sets, so I got nervous about future stock and went ahead and grabbed a set.

Thanks for your order. I have been selling a bunch of them. 3 sets over the weekend. I just ordered 5 more sets today.

Brian

Thu Mar 20, 2025 12:42 pm

It's been at least 20 years since I've read a micrometer without a digital readout.

Since the range of micrometers needed to accurately measure everything in the engine is only covered by my old set that haven't been out of the box in that 20 years, it took me a while to re-teach myself how to read one with .0001" resolution. Now that I've miked my new crank several times to get consistency I think I've got the ability to use them again.

I've picked up a 2"-6" dial bore gauge for the cylinders, (hoping to pick up a set of Ps and Cs tomorrow) rod big ends, main bearing bores, but won't cover the lifter bores and the cam bearing bores. Not really looking to pick up another dial bore gauge if possible.

I figure I might be able to do a go/no-go on the lifter bores with an old-school inside caliper and aforementioned micrometers, but what to do about the cam bearings?

Ok to use .001-.003" green plastigauge once the cam comes in? Or do we need to be more accurate than that?

Thanks in advance!

Thu Mar 20, 2025 2:00 pm

Rob Combs wrote: It's been at least 20 years since I've read a micrometer without a digital readout.

Since the range of micrometers needed to accurately measure everything in the engine is only covered by my old set that haven't been out of the box in that 20 years, it took me a while to re-teach myself how to read one with .0001" resolution. Now that I've miked my new crank several times to get consistency I think I've got the ability to use them again.

I've picked up a 2"-6" dial bore gauge for the cylinders, (hoping to pick up a set of Ps and Cs tomorrow) rod big ends, main bearing bores, but won't cover the lifter bores and the cam bearing bores. Not really looking to pick up another dial bore gauge if possible.

I figure I might be able to do a go/no-go on the lifter bores with an old-school inside caliper and aforementioned micrometers, but what to do about the cam bearings?

Ok to use .001-.003" green plastigauge once the cam comes in? Or do we need to be more accurate than that?

Thanks in advance!
I feel your pain on re-learning how to read micrometers. Every time I get mine out of the box, I have to relearn how to properly read them. It makes my head hurt.

On your dial bore gauge, what is the resolution of the gauge? I made the mistake of buying set the were .00005". Talk about having to do some extra curricular math. :shock:

Thu Mar 20, 2025 2:12 pm

Bore gauge resolution is .01mm. So, some additional metric to inches conversion math to be done there too, but that's not too bad.

The challenge I've got right now is that the dial bore starts at 50mm (~ 2"), so it's fine for the crank bearings but won't fit into the smaller bores like the cam bearing bore.

Hence the question about whether we find it ok to use green plastigauge as opposed to buying another (far more expensive) small dial bore gauge, if limited to the cam bore...

Thu Mar 20, 2025 2:23 pm

Never tried Plasti-gauge on the cam bearings.
You can use a set of "Snap" gauges from HF to get the measurements you're seeking. Of course, you'll need a 1" micrometer to read the Snap gauge spread.

Thu Mar 20, 2025 2:28 pm

67rustavenger wrote: Never tried Plasti-gauge on the cam bearings.
You can use a set of "Snap" gauges from HF to get the measurements you're seeking. Of course, you'll need a 1" micrometer to read the Snap gauge spread.

Yea I have a set of those - now I know why they're so maligned in the precision measurements community. It was damn near impossible to get repeatable measurements within .002" in the lifter bores on my beat up practice case, which is about where we need our oil clearances on the cam bearings, so I don't trust them, or at least don't trust myself with them. I got more consistent results with a very old inside caliper and a micrometer, and I may have to settle for that.

Could easily be operator error though...

Thu Mar 20, 2025 2:43 pm

It's not you Rob. They are a PITA.
I'm not gonna sweat .001-.002" on a cam bearing or lifter bore. Well maybe the lifter bore, a little.

You can use a dial indicator to see if the lifter bores are a little worn.
Install the lifter and use the dial gauge to read the wiggle of the lifter head in the bore. I hope that makes sense.

Thu Mar 20, 2025 2:45 pm

Yes that makes sense - the old wiggle test.